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EVALUATIVE MOVEMENT ASSESSMENT (EMA) - keyboard responses
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Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 05-03-2016
last updated: 04-26-2024 by K. Borchert (katjab@millisecond.com) for Millisecond Software, LLC
Script Copyright © 04-26-2024 Millisecond Software
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BACKGROUND INFO
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This script implements a version of the Evaluative Movement Assessment (EMA) procedure.
The EMA is a response time measure of implicit evaluations. Specifically, this script is designed as a template
and assesses people's implicit attitudes towards "weekend", "mosquito", and "airport" using well established
EMA targets "cavities" and "movie theaters" as attitude calibration targets.
It is suggested that the calculated EMA scores for several target categories
1) help rank the evaluations on a single scale
2) provide a neutral preference point for the scale
Reference:
Miguel Brendl, C.M, Arthur B. Markman, A.B. & Messner, C. (2005).
Journal of Experimental Social Psychology, 41, 346–368.
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TASK DESCRIPTION
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Participants are asked to move words (targets and distractors) -that are displayed either to the right or
left of their own name- either towards or away from the name. In this script, participants move
the stimuli by repeatedly pressing a left or right response button which 'moves' the stimuli
visually closer or father away from the name.
Targets: all towards (or all away; depending on block instructions)
Distractors: towards/away depends on valence of word
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DURATION
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the default set-up of the script takes appr. 30 minutes to complete
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DATA OUTPUT DICTIONARY
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The fields in the data files are:
(1) Raw data file: 'evaluativemovementassessment_raw*.iqdat' (a separate file for each participant)
build: The specific Inquisit version used (the 'build') that was run
computer.platform: the platform the script was run on (win/mac/ios/android)
date, time: date and time script was run
subject, group: with the current subject/groupnumber
session: with the current session id
blockCode, blockNum: the name and number of the current block (built-in Inquisit variable)
trialCode, trialNum: the name and number of the currently recorded trial (built-in Inquisit variable)
Note: trialNum is a built-in Inquisit variable; it counts all trials run; even those
that do not store data to the data file.
countBlockTrial: trialCounter per block
stimType: "target1"/"target2"/"target3"/"target4"/"target5", "distractor", "calibration","filler"
direction: stores the direction in which the current word should be moved in relationship to the name ("towards" vs. "away")
stimPosition: "left": word is presented on left side of the screen; "right": word is presented on right side of the screen
stimX: stores the x coordinate of the stimulus
correctMovement: stores the direction the current word should be moved ("left" vs. "right")
valence: stores the valence of the currently presented word ("positive", "negative", "")
stim: stores the currently presented word
acc: stores whether the initial movement is in the correct direction (irrespective of latencies and later movement changes)
rt: stores the latency (in ms) of the initial movement measured from onset of words to pressing the response button
valid: 1 = initial response was correct, within the responsewindow, and movement direction stayed the same throughout
0 = otherwise
initial Move: stores the direction of the initial movement (left vs. right)
Direction Change: true = participant changed movement direction; false = participant did not change movement direction
testData: 0 = data not considered as test data (= practice); 1 = data considered as test data
(2) Summary data file: 'evaluativemovementassessment_summary*.iqdat' (a separate file for each participant)
inquisit.version: Inquisit version run
computer.platform: the platform the script was run on (win/mac/ios/android)
startDate: date script was run
startTime: time script was started
subjectId: assigned subject id number
groupId: assigned group id number
sessionId: assigned session id number
elapsedTime: time it took to run script (in ms); measured from onset to offset of script
completed: 0 = script was not completed (prematurely aborted);
1 = script was completed (all conditions run)
propCorrectAll: overall proportion correct for the 4 main blocks based on performance in distractor, targets and calibration target trials
medianRTAll: overall median latency (in ms) of correct responses for the 4 main blocks based on distractors, targets and calibration trials
meetsExclusion: returns 1 if participant's error rate exceeds parameters.exclusionCriterium (default: errorate > 0.07)
cc: calibration coefficient as the difference of the two to estimate the positivity bias of the participant
positivity bias: the tendency to be faster when moving a word towards the name than away from it
(even if both directions are congruent with the valence of the word)
calculated as the difference between the mean of the away latencies of the calibration targets
and the mean of the toward latencies of the calibration targets (here: target 4 and target 5)
medianRTTarget1Away: median latency (in ms) of correct responses for moving target1 away from the name
medianRTTarget1Towards: median latency (in ms) of correct responses for moving target1 towards the name
emaTarget1: EMA score for target1; difference in away and towards median latency corrected by the calibration coefficient
medianRTTarget2Away: median latency (in ms) of correct responses for moving target2 away from the name
medianRTTarget2Towards: median latency (in ms) of correct responses for moving target2 towards the name
emaTarget2: EMA score for target2; difference in away and towards median latency corrected by the calibration coefficient
medianRTTarget3Away: median latency (in ms) of correct responses for moving target3 away from the name
medianRTTarget3Towards: median latency (in ms) of correct responses for moving target3 towards the name
emaTarget3: EMA score for target3; difference in away and towards median latency corrected by the calibration coefficient
medianRTTarget4Away: median latency (in ms) of correct responses for moving target4 away from the name
medianRTTarget4Towards: median latency (in ms) of correct responses for moving target4 towards the name
emaTarget4: EMA score for target4; difference in away and towards median latency corrected by the calibration coefficient
medianRTTarget5Away: median latency (in ms) of correct responses for moving target5 away from the name
medianRTTarget5Towards: median latency (in ms) of correct responses for moving target5 towards the name
emaTarget5: EMA score for target5; difference in away and towards median latency corrected by the calibration coefficient
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EXPERIMENTAL SET-UP
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1 practice block of 24 trials: only distractor items (12 positive, 12 negative; randomly selected from the list of distractors)
5 EMA blocks run in a AABBA/BBAAB within subjects design (performance during the first A block is not considered for calculation of EMA scores)
(order is counterbalanced by groupnumber)
Each EMA block: 83 trials
- 5 Targets tested (each with one target word) - each repeated 7 times = 35 target trials
Note: the odd number of trials results in the targets being unequally often left or right to the name.
For each participant, it's decided randomly whether the targets are more often left than right to the name.
- 40 distractor items (20 positive, 20 negative) - each repeated once = 40 distractor trials
- 4 filler items (2 positive, 2 negative) - each repeated 2 times (used as prefatory trials before start of block and after rest period) = 8 filler trials
- each block presents a rest trial in the middle (block starts again with 4 filler trials)
Block Sequence:
- 4 filler trials
- 38 randomly selected trials from targets, distractors
- rest trial
- 4 filler trials
- 37 randomly selected trials from targets, distractors
Trial Sequence:
blank (600ms)->name in white frame + 4 XXXX (700ms)->XXXXmask replaced by red attitude word-> wait for response -> potential error feedback
EMA Score Calculation: EMA scores are based on the difference in median latencies of away and toward movements corrected by a calibration constant
Positive Response Bias (positivity bias): participants tend to be faster in moving stimuli towards their names than away from their names
regardless of valence of target words
=> Diff (awayRT - towardsRT) tend to be positive (which affects the neutral point evaluation though not the relative ranking of 'preferences')
=> correction/calibration necessary
Calibration Algorithm applied in this script:
1) run known (2) target words as calibration targets; these target words need to roughly have a mean valence rating of 0
(here: 'movie theater' and 'cavities', see Brendl et al, 2005)
2) establish calibration constant: CC = meanRT(away) - meanRT(towards) for the two calibration targets
(if no bias towards 'towards' movements, one would expect CC = 0 with the selected calibration targets)
3) Use calibration constant in EMA score calculations:
EMA(target1) = median(away_target1) - median(towards_target1) - CC
EMA(target2) = median(away_target2) - median(towards_target2) - CC
EMA(target3) = median(away_target3) - median(towards_target3) - CC
EMA(target4) = median(away_target4) - median(towards_target1) - CC (=calibration target) => 0
EMA(target5) = median(away_target5) - median(towards_target1) - CC (=calibration target) => 0
based on: (awayRT-CC/2) - (towardsRT + CC/2) = awayRT - towardsRT - 2*CC/2 = awayRT - towardsRT - CC
Removal of error trials for calculation of EMA scores:
- only latencies of correct initial responses within the set response window (between 100-3000ms after onset of words)
and without response reversals are considered for EMA score calculations
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STIMULI
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see section Editable Stimuli
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INSTRUCTIONS
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provided by Millisecond Software as htm-files (htm files can be edited with Notepad (Windows) or TextEdit (Mac))
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EDITABLE CODE
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check below for (relatively) easily editable parameters, stimuli, instructions etc.
Keep in mind that you can use this script as a template and therefore always "mess" with the entire code
to further customize your experiment.
The parameters you can change are:
Response Keys: Tools-> Keyboard Scancodes
/responseKeyLeft: the left response button (default: "A")
/responseKeyRight: the right response button (default: "L")
/nameSize: the fontheight in canvas height percentages of the name stimulus (default; 4%)
/nameLeftx: the left horizontal screen position in canvas width percentage of the name/stim (default: 30%)
/nameRightx: the right horizontal screen position in canvas width percentage of the name/stim (default: 70%)
/blankDuration: the duration of the blank screen (in ms) at beginning of trial (default: 600ms)
/xxxxDuration: the duration of the XXXX mask (in ms) (default: 700ms)
/mInvalidResponseLatency: the duration of the minimum valid response latency in ms; measured from onset of targets (default: 100ms)
/maxValidResponseLatency: the duration of the maximum valid response latency in ms; measured from onset of targets (default: 3000ms)
/iti: intertrial interval in ms (default: 0)
/exclusionCriterium: sets the overall error rate in the testblocks that would exclude a participant from further analyses (default: 0.07)
Note: if the error rate indicates exclusion from analyses,
the summary data file stores a '1' under expressions.meetsExclusion
